From the start to the big finish

Evolution is undergoing a revolution. We are eliminating species probably 100,000 times faster than the background rate before the arrival of humans. Still more significantly, we are effectively though unknowingly disrupting some of the basic processes of evolution. It is as if we are poking a huge stick into evolution's workings and giving the whole thing a thorough stir.

Conservation considerations apart, evolution experts should be delighted with this unprecedented planet-wide experiment with evolution. It is comparable in many respects to a chance to witness the circumstances of the "great dying" 65 million years ago when the dinosaurs and associated species were eliminated, probably reducing the planet's biodiversity by a whopping half. Yet there is apparently scant interest in this extraordinary phenomenon in the leading evolution journals. Indeed one gains the impression that we live in a world that is going its usual tranquil way with next to no perturbations of even moderate moment. Of course evolutionists can respond that their discipline has to be, virtually by definition, a retrospective affair. What is the point anyway, and where is the science, in speculating about the future?

All the more power to Peter Ward for taking a look at what the current biotic crisis might do to evolution. In an authoritative and eclectic book, he proposes that we are engaging in what he calls "The Third Event". The other two were mass extinctions 250 and 65 million years ago, events that in scope and scale exceeded all the other 13 such episodes. They not only knocked off large numbers of species but profoundly reorganised ecosystems at sea and on land. This time, too, Ward asserts, "life on the Earth will be forever changed".

The book takes us on a journey through geologic time, starting with the beginnings of major life almost 600 million years ago. We hear about the Paleozoic and Mesozoic Eras, ended by the spectacular species crashes cited above. We then move on to the Cenozoic Era, which is being ended by the present biotic holocaust. Along the way we get a detailed account of the dinosaurs' demise: Ward does a fine job with the what, when and how of that evolutionary parting of the ways, dealing as much with the aftermath (especially the radiation of mammals) as with the cataclysm itself.

The book then moves on to the late Pleistocene overkill by human hunters, when North America, South America and Australia lost three-quarters of their mammal genera. More recently still comes the relatively instantaneous elimination on Pacific islands of 1,000 bird species, a tenth of the world's avifauna (some scientists think twice as many), during the past two millennia. Finally the book brings us to the present stage, mainly from 1950 onwards, when a full-scale catastrophe has started to overtake the planet's biotas.

Ward is not altogether correct in saying, as in his title, that this latest debacle will mean the end of evolution. He rightly observes that the mass extinction under way "will not eliminate life from the Earth: no mass extinction does that". If all that remained were cockroaches, horseshoe crabs, bugs and assorted pests and weeds - creatures that have survived many environmental vicissitudes in the past, or that thrive in humans' shadow - they would still present enough raw material for natural selection to work its evolutionary way, albeit in severely depauperate form. Ward attempts an exploratory appraisal of what this will mean for evolutionary processes, but he does not venture far into this unknown territory. It is a pity he is not adventurous enough to engage in some creative speculation about what evolutionary departures might lie ahead.

Nor does he argue the "responsibility case" as strongly as he might. We are surely disrupting evolution for five million years to come, possibly longer, this being the period required for evolution to generate a replacement stock of species to match what we have today in abundance and diversity. Yet we are imposing this biosphere impoverishment upon a minimum of 200,000 future generations, or 20 times more than the number since humans themselves emerged as a species. Worse, we are doing it with hardly a thought of what we are about. All the more thanks to Ward, then, for probing the prospect.

The reservations notwithstanding, this is a book with fine insights into evolution's workings. Ward draws upon his research in areas ranging from Hawaii to South Africa to show how evolutionary mechanisms operate - and how we are throwing multiple spanners into the works. I recommend his book to all who cast an inquiring eye over our world as it undergoes one of the greatest upheavals since the emergence of major life 600 million years ago, an upheaval that will largely occur within just another 60 years.

Norman Myers is honorary visiting fellow, Green College, University of Oxford.